A range of geophysical sensors are available to look through the ground to better understand the ground conditions or detect buried features such as pipes, cables, foundations, mineshafts but they all have limitations with respect to resolution and depth penetration.
Many of these techniques require a signal to be induced into the ground with the response measured, such as electromagnetic waves for GPR, but these are naturally attenuated by the ground, especially in conductive soils such as clay (see also our geophysics research capability). Gravity sensors overcome these limitations as they rely on measuring a passive response from the targets which cannot be blocked, shielded or attenuated, but current technology is limited in accuracy and by vibrational noise in the environment.
Research at the University of Birmingham has concentrated on developing a quantum technology (QT) gravity gradiometer sensor since 2010 in a collaboration between colleagues from the School of Physics and Astronomy and the School of Engineering. The QT sensor uses rubidium atoms as test masses and a laser as a ruler exploiting the quantum effect of the atoms existing in two different energy stages at the same time (see UK Quantum Technology Hub Sensors and Timing). The advantage of the QT gravity gradiometer is that it can suppress external noise sources such as vibrations from wind, tides, traffic much better than existing sensors thereby allowing operations in a much more hostile (noisy) environment while also allowing faster surveys with a higher sensitivity compared to existing sensors.
The sensor has been evaluated in a number of engineering experiments and benchmarked against existing sensors. In a world-first, the cold-atom QT gravity gradiometer detected a buried multi-utility tunnel on the University of Birmingham’s campus. The QT sensor was tested in the National Buried Infrastructure Facility where we evaluated its performance of detecting a buried pipe in our large-scale sand pit. We successfully demonstrated that the QT sensor is able to successfully suppress noise compared to the standard mass on a spring instrument. Moreover, work has evaluated the potential of the QT sensor in a number of engineering applications. These included evaluating the potential of the new sensor to detect drainage features under railway lines, wetbeds or badger burrows in QT-PRI as part of a collaboration with RSK, Network Rail and Atkins.
- Stray, B., Lamb, A., Kaushik, A., Vovrosh, J., Rodgers, A., Winch, J., Hayati, F., Boddice, D., Stabrawa, A., Niggebaum, A., Langlois, M., Lien, Y-H., Lellouch, S., Roshanmanesh, S., Ridley, K., de Villiers, G., Brown, G., Cross, T., Tuckwell, G., Farmarzi, A., Metje, N., Bo ngs, K., Holynski, M. (2022). Quantum sensing for gravity cartography. Nature 602, pp. 590–594. https://doi.org/10.1038/s41586-021-04315-3
- Boddice, D., Metje, N., Tuckwell, G. (2019). Quantifying the Effects of Near Surface Density Variation on Quantum Technology Gravity and Gravity Gradient Instruments. Journal of Applied Geophysics. Vol. 164, pp. 160-178.
- Boddice, D., Metje, N., Tuckwell, G. (2017). Capability Assessment and Challenges for Quantum Technology Gravity Sensors for Near Surface Terrestrial Geophysical Surveying. Journal of Applied Geophysics, Vol. 146, pp. 149-159.